Mask identification systems

ABSTRACT

A mask identification system according to which a mask indication is originated having three parts: one first part specifically meant to indicate the length of a slice; a second part specifically meant to indicate the origin of this slice; a third part which will either complete the first part, in order to characterize the lengths of larger slices (the value which characterizes the origin of the slice being then necessarily small), or it will complete the second part, in order to characterize the origins of upper ranks (the value characterizing the length of the slice being then necessarily small), so that most of the values that the mask indication take up in its entirety are effectively utilized and the number of digits making up this indication are limited to a minimum.

United States Patent Inventors Roger A. Pain Vaires; Serge Delaigue, Virotlay; Pierre Ii. Cogne, Saint-Maur, all of, France Appl. No. 841,763 Filed July [5, I969 Patented Aug. 31. 197i Assignee international Standard Electric Corporation New York, N.Y. Priority Aug. 2, 1968 France 16 I 600 MASK IDENTIFICATION SYSTEMS 5 Claims, 3 Drawing Figs.

[56] References Cited UNITED STATES PATENTS 3,35l,9l5 ll/l967 Fought etal .r 340/1726 ABSTRACT: A mask identification system according to which a mask indication is originated having three parts: one first part specifically meant to indicate the length of a slice; :1 second part specifically meant to indicate the origin of this slice; a third part which will either complete the first part, in order to characterize the lengths of larger slices (the value which characterizes the origin of the slice being then necessarily small), or it will complete the second part, in order to characterize the origins of upper ranks (the value characterizing the length of the slice being then necessarily small), so that most of the values that the mask indication take up in its entirety are effectively utilized and the number of digits making [46.2 up this indication are limited to a minimum.

s ffipfi 0555/11 5 l 1 i L I M i i 0,02: M E/ w Z t LA- (.L A I DP/ 7 DPHO 16 B7 MASK IDENTIFICATION SYSTEMS BACKGROUND OF THE DISCLOSURE The present invention concerns improvements to systems which designate the masks used, namely. in digital computers; and it aims particularly at a process enabling the designation of these masks by means of numbers which include as few digits as possible in a given notation, and, specially, in the bi= nary notation.

In the related application Ser. No. 840,660 filed July 10, [969, there is described how digital computers will process words made up by the juxtaposition of a certain number of binary information elements or bin; and, how they will more particularly process parts of words so-called slices," that is to say, groups of bits selected inside words by means of masks.

By way of example, it can be assumed that a data word is a group of I6 bits numbered from to IS. Whatever a slice would be for instance, inside the word, the group of four bits bearingthe numbers 8, 9, I0, I]. In order to select this slice, there is from 0 word of I 16 bits, so-called mask, all the bits each, which have 0 for value, except the bits 8, 9, I0, I l which obtain the value 1. There is then immediately seen that it would just be necessary to combine the data word and the mask in order to select the considered slice.

Selection of a slice, thus, resumes itself to the originating of the appropriate mask; this however requires a system identifying the masks.

According to the related application, a slice can be designated by: (a) its length, and (b) its origin in the word. These two indications, in the case of the foregoing example, correspond, the one, to the number of bits of the slice 4 and the other to the rank of the first bit of the slice 8. They can each take up all the values from 0 to (in decimal notation) and will therefore require, each four bits (in binary notation). Thus the identity of a mask would require eight bits.

SUMMARY OF THE INVENTION The present invention provides improvements to mask identification systems aimed at limiting to a minimum the number of digits, or bits in binary notation, which are necessary for identifying a slice. It is applicable in a general way, whatever might be the number of elements of the word and the adopted base of notation. It can be applied, especially, in the digital computers and will make it possible, by reducing the length of the indications that identify the masks, to liberate bits which will be utilizable for other functions, or, to limit the size and price of the memories, as well as the circuits, taking care of these indications. The present invention thus enables reaching that result without restricting the number of possible masks.

One feature of the invention is a mask identification system, according to which a mask indication is being provided, made up of three parts: a first part specifically meant for indicating the length of the slice; a second part specifically meant for indicatihg the origin of the slice; a third part that will either complete the first part, for characterizing the lengths of larger slices (the value, characterizing the origin of the slice, being then necessarily small), or will complete the second part, for characterizing the origins of upper ranks (the value, characterizing the length of the slice being then necessarily small), so that most of the values which the mask ihdication can take as a whole should effectively be utilized and that the number of digits making up this indication should be limited to a minimum.

Another feature of the invention, in an application of the invention making use of the binary notation, the above-mentioned third part is a complementary bit which will complete either the above-mentioned first part (length of the slice), by juxtaposition, on the heavy weights side, or the second part (origin of the slice), also by juxtaposition, on the heavy weights side.

Still another feature of the invention, when the complementary bit has 0 for value, the said first part will indicate directly the length of the slice, whereas the said second part will indicate directly the origin of the slice.

According to another feature of the invention, when the complementary bit has 1 for value, the combined values of the first and second parts are examined and, if their total is lower than a certain value, the complementary bit is routed so as to complete the first part; whereas, if their total is higher than a certain value, the complementary bit is routed so as to complete the second part.

BRIEF DESCRIPTION OF THE DRAWINGS Other features of the invention will become apparent from the description that follows taken in conjunction with the accompanying drawings in which:

FIG. 1 a data word inside which is delimited a slice;

FIG. 2, a table illustrating how, according to the invention, it is possible to identify the masks corresponding to the various slices which can be cutout inside the word of HG. l; and

FIG. 3, a circuit for the conversion of mask indications.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. I shows a data word MD comprising l5 bits numbered from 0 to 14 and in which a slice TR has been delimited (hatched part) that is made up by the bits of ranks 7 to 12. As is indicated in the above-mentioned application, this slice can be identified by an indication BT giving the rank of the first bit of the slice (B7=7) and by an indication LG giving the number of bits of the slice (LG==6). This system enables identifying a slice. The indication of origin 87 can take up all the possible values from 0 to l4 and the indication of length LG can take up all the possible values from I to 15. Each of these indica tions, in binary notation, will require four bits, that is eight bits for the indication of slice which is also the identity of the mask enabling to select it.

The present invention enables reducing the number of digits of this identity of mask. It is first worth noting that, since a slice is always contained in the word, the rank of the last bit of the slice is, at the most, the rank of the last bit of the word; in the example in FIG. I, the total of the indications BT and LG cannot exceed 14. This means that the number of different slices is not 15x15, but l+2+3...+15, that is 120, as will be seen by referring to FIG. 2.

FIG. 2 is a table illustrating, on the one hand, the number of different possible slices, in the case of FIG. 1, and, on the other hand, a particular application of the system of mask identification of the present invention. The columns of this table correspond to the different values which the indication of origin BTcan take, whereas the rows correspond to the different values which the indication of length LG can take up.

It is seen that when BT=0 (origin to bit 0), the length of the slice can take up all the values, from 1 to 15. Whereas, if BT=l, LG cannot exceed l4. Without that, the slice would extend beyond the word. Likewise, if BT=2, LG cannot exceed l3, and so on, until BT=l4, which imposes LG=l. The maximum number of different slices is therefore indeed equal to 120. This number is lower than 2'=l28. Consequently, it is possible to designate each slice by a 7 instead of 8-bits indication, as was mentioned above.

Inside each compartment in the table, a number is written down which is made up of three digits and expressed in octal notation. In practice, the two digits on the right can take up all the values between 0 and 7 and are each expressed by three hits, in binary notation. Whereas, it is seen that the digit on the made up of the digit on the right, specifically assigned to the origin indication, and a complementary bit which makes up the digit on the left.

In referring to the table in FIG. 2. it is quite clear that as long as the length does not exceed 8, the central digit is enough for defining it. Likewise. as long as the origin does not exceed 7, the digit on the right will be enough for defining it. The complementary bit has, then, the value 0, and does not intervene in the indication.

Then, when the length exceeds 8, the complementary bit takes up the value I; and it is assigned for completing the length indication (central digit). It could be considered that it would place itself on its left. This, then, will enable composing the values ID to l6, in octal notation, which characterize the lengths from 9 to 15.

There now remains to define the masks, the origin of which has a value higher than 7. The complementary bit will still have the value 1 and will be utilized, this time, to complete the origin indication provided by the digit on the right. Yet, since there is forcibly excluded to make use of already utilized mask indications, it would be agreed, moreover, to change the two digits on the right into their complement to 7. Indeed, on the first row (LG=l the mask indications, after 007, should normally be I00, I01, I02.... It is seen that dtese indications already serve for LG=9. In replacing the two digits on the right by their complement to 7, there will be obtained I77, I76, I75 These indications are available because they correspond to combinations not utilized for origin values going from O to 7.

More simply speaking, if the table of combinations is being considered, which is utilized practically for the origin values going from to 7 the entirety of which makes up an area M, it is immediately seen that this table is incomplete. To complete it, it is necessary to addzl07; ll6, l l7: 125, I26, I27; etc. In this complement, a triangular area M is delimited and is transferred, by rotation, to the right of area M, and would provide the necessary combinations.

It may be seen, when the complementary bit has 1 for value, that a combination can be in area M or in area M (or be nonutilized It is easy to know this by adding up the two digits on the right. if the total is equal to or lower than 6, the combination would belong to the area M, if it is equal to or higher than 8, the combination would belong to area M.

It is quite evident that the system of the present invention can be applied, in as much, to words (FIG. I) of different lengths. It would just be necessary to draw a table similar to the one of FIG. 2 and according to the same principles, but with appropriate numbers of rows and columns. It is moreover possible to limit, by a contrivance, the number of different possible slices, in order to facilitate applying the present invention. For instance, if the word has l6 bits it may be agreed not to process the slice of only one bit within the mask identification system. This leads back to the case of a word of bits illustrated by FIGS. I and 2 with the one difference only that the rows in the table of FIG. 2 instead of corresponding to LG=l to Is would correspond to LG=2 to l6.

Now will be described, by referring to FIG. 3, circuits making it possible to convert the 7-bits mask indications into 8-bits mask indications apt to control the mask circuits of a computer, as indicated in the related application for patent mentioned above.

The digit on the right of the indications in FIG. 2 is provided by the three bits A, B, C and their respective complements K, i, if. Likewise, the central digit is provided by the bits D, E, F and their complements 5, E, F. The com lementary bit is G. Finally, an analysis circuit, not shown in t e figure, provides a signal M when an indication to be translated belongs to the area M in the table of FIG. 2, or a signal M, when it belongs to the area M.

The transmission of the bit A is conditioned by a gate pit, and AND type, controlled by M. It can be seen that an AND gate is simply represented by a small diagonal stroke at crossing of A and M. Likewise, the transmission of A is condirepresent decoupling diodes) providing a signal DPHO which may correspond either to A or to K.

It is immediately seen, therefore, that if M is provided, the 7-bits input combination, G to A, will provide a 4-bits indication LG corresponding to G, F, E, D--that is to say, to the central digit of FIG. 2, completed by the complementary bit (digit on the left) and a 4-bits indication BT whose three digits on the right correspond to C, B, A, and the one on the left is null (since p14 is blocked). On the contrary, if M is provided, the indication LG will correspond to F, E, 5 (complement to 7 of t he central digit) and the indication BT will correspond to G, C, B, A (complement to 7 of the digit on the right, increased by the complementary bit).

The circuits helping to originate the signal M will not be described here. In the case of the example illustrated by FIG. 2, the corresponding logic function is, strictly:

The logic function corresponding to M is similar. In practice, it can be attempted to originate M only, and, to deduce thereof M by inversion. The only consequence would be having the nonutilized combinations not being taken into account; but this in fact does not prove a hindering disadvantage. It is even possible to take advantage of these nonutilized combinations by classifying them in M or in M, so as to simplify the logic function providing M (or M).

We claim: I. A mask generating circuit comprising: me ans for analyzing a combined mask indication (A-G, A G) and producing either a condition (M) or a complementary condition (M);

means (ptl) responsive to said condition (M) for translating the combined mask indication (A-G, K-G) into three parts (A-C, D-F, G) and for generating an origin indication (BT) which is equal to the first part (A-C) and a length indication (LG) which results from the juxtaposition of the second part (D-F) and of the third part (G); and

means (p12 and p24) responsive to said condition (M) for translating the combined mask indication (A-G, K-G) into three parts (A-C, D-F, G) by generating an origin indication (BT) which re sults from the juxtaposition of the inverted first part (X-C) and of the third part (G) and a length indication (LG) equal to the inverted second part.

2. The circuit of claim 1 wherein said means (prl) comprise AND gates.

3. The circuit of claim 2 wherein said means (p12 and p14) comprise AND gates.

4. The circuit of claim 3 wherein said means (ptl) and (p82) have their outputs coupled by OR gates.

5. In a mask identification system wherein a slice of a data word is specified by a two-part slice indication, a process for providing a mask indication comprising:

indicating the number of bits in a slice',

indicating the place of the slice in a data word;

coding the two separate indications into one combined slice indication; and

decoding the combined slice indication to produce the two-.

part slice indication, whereby the combined slice indication is shorter than the two-part slice indication. 

1. A mask generating circuit comprising: means for analyzing a combined mask indication (A-G, A-G) and producing either a condition (M) or a complementary condition (M); means (pt1) responsive to said condition (M) for translating the combined mask indication (A-G, A-G) into three parts (A-C, D-F, G) and for generating an origin indication (BT) which is equal to the first part (A-C) and a length indication (LG) which results from the juxtaposition of the second part (D-F) and of the third part (G); and means (pt2 and pt4) responsive to said condition (M) for translating the combined mask indication (A-G, A-G) into three parts (A-C, D-F, G) by generating an origin indication (BT) which results from the juxtaposition of the inverted first part (A-C) and of the third part (G) and a length indication (LG) equal to the inverted second part.
 2. The circuit of claim 1 wherein said means (pt1) comprise AND gates.
 3. The circuit of claim 2 wherein said means (pt2 and pt4) comprise AND gates.
 4. The circuit of claim 3 wherein said means (pt1) and (pt2) have their outputs coupled by OR gates.
 5. In a mask identification system wherein a slice of a data word is specified by a two-part slice indication, a process for providing a mask indication comprising: indicating the number of bits in a slice; indicating the place of the slice in a data word; coding the two separate indications into one combined slice indication; and decoding the combined slice indication to produce the two-part slice indication, whereby the combined slice indication is shorter than the two-part slice indication. 